package org.stianloader.mrjmania;

import java.net.URL;
import java.net.URLClassLoader;

import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

/**
 * Polyfill for the {@link URLClassLoader} regarding the fact that classloaders
 * can be named in Java 9 and beyond.
 *
 * <p>In Java 8 this doesn't do much, but in Java 9+ the classloader's name will show
 * up in stacktraces, which is very helpful for diagnosing certain classloading errors.
 *
 * <p>This classloader is parallel-capable.
 */
public class MRJURLClassLoader extends URLClassLoader {

    /**
     * Returns the name of the given classloader. For Java 8,
     * this method only returns for classloaders that are an instance of {@link MRJURLClassLoader}.
     * Otherwise, it returns {@code null}.
     *
     * <p>For Java 9 and above, it returns a value for any {@link ClassLoader},
     * provided said {@link ClassLoader} has been assigned a name.
     *
     * @param loader The {@link ClassLoader} instance to get the name of.
     * @return The name of the given loader.
     */
    @Nullable
    public static final String getClassloaderName(ClassLoader loader) {
        return loader.getName();
    }

    /**
     * Obtains the platform classloader under Java 9 or above. Under Java 8, {@code null} is returned.
     *
     * <p>Keep in mind that while the platform classloader contains the platform classes, it has also
     * access to modules on the modulepath. This means that when using JPMS/Jigsaw, it may load classes
     * that are part of the 'app' classloader. This behaviour contradicts the behaviour for classes
     * present on the classpath, which cannot be loaded through the platform classloader.
     *
     * @return The platform classloader, if present.
     */
    @Nullable
    public static final ClassLoader getPlatformClassLoader() {
        return ClassLoader.getPlatformClassLoader();
    }

    /**
     * Constructor.
     *
     * @param name The name of the {@link ClassLoader}.
     * @param urls The URLs for the {@link URLClassLoader}, see {@link URLClassLoader#getURLs()}.
     * @param parent The parent classloader, see {@link ClassLoader#getParent()}.
     */
    public MRJURLClassLoader(@NotNull String name, URL @NotNull[] urls, @Nullable ClassLoader parent) {
        super(name, urls, parent);
    }

    static {
        ClassLoader.registerAsParallelCapable();
    }
}